Research methods: Cross-sectional and longitudinal designs



Studying a cross-section (slice) of the population at one time point

Widely used because it’s cost-effective and quick

However, it’s difficult to compare different age groups because we are also comparing different individuals

It’s unsure if the changes are definitely due to maturational process or explained by differences between groups

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Following the same subjects over time

Repeated measures

Developmental psychology: changes across the lifespan

Other areas of psychology: temporal associations (the timings of associations)

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A sample that is very large and intended to be representative 

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Cohort effects

When results are due to cohort: experiences of those born in different decades, that we are studying different individuals

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Cross-generational problem

long-term changes in the environment may limit conclusions of a longitudinal project to that generation of children who were growing up while the study was in progress

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Practice / test effect

being exposed to the same test too many times, may lead participants to remember/know/learn/understand/improve at the test

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Selective survival

challenge with studying older age or certain health conditions, they start dying

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Selective drop-out / attrition

Loss of participants from sample over time, as they choose to leave the study

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Cross-sectional, short-term longitudinal study

A compromise design which uses aspects of both cross-sectional and longitudinal studies

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Cross-lagged correlations

 refers to a study in which two variables are measured once and then again at a later time

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A prospective cohort study is a longitudinal cohort study that follows over time a group of similar individuals who differ with respect to certain factors under study, to determine how these factors affect rates of a certain outcome

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The retrospective cohort study compares groups of individuals who are alike in many ways but differ by a certain characteristic in terms of a particular outcome

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